This application claims the benefit of German patent application DEP10022736.8, filed May 10, 2000, herein incorporated by reference.
The present invention relates to a method of operating a magnetic bearing arrangement for an open-end spinning device and to a corresponding magnetic bearing arrangement.
In the spinning devices of modern open-end spinning machines, various types of specific embodiments are known for supporting spinning rotors that rotate at a high speed. Most of the open-end spinning machines currently on the market comprise spinning rotors that are supported with their rotor shaft in the bearing nip of a so-called support disk bearing. It is customary in such support disk bearings to provide an addition axial bearing for axially fixing of the spinning rotor, which axial bearing can be designed either as a mechanical bearing or as a magnetic bearing. Such bearing arrangements permit rotor speeds of greater than 100,000 revolutions per minute.
Even though these support-disk bearing arrangements have proven themselves in practice, they have the disadvantage that they are subjected to significant mechanical strain, especially in the area of the running surfaces of the support disks. The pressing operation occurring in these areas results on the one hand in a not insignificant wear and on the other hand in energy losses. Therefore, attempts have already been made in the past to support such spinning rotors without wear while rotating at high speed.
For example, German Patent Publications DE-OS 28 18 255, DE 31 30 974 A1 or DE 198 27 606 A1 describe spinning rotors that are driven by an individual motor and are supported in a contactless manner in appropriate magnetic bearing arrangements.
German Patent Publication DE-OS 28 18 255 describes a magnetic bearing arrangement comprising at least one ring-shaped or disk-shaped permanent magnet on the stator side and on the rotor side. The permanent magnets are arranged in such a manner that repelling magnetic bearing forces are active between rotor and stator. In addition, electric windings are provided between the permanent magnets of the stator via which windings the magnetic force can be strengthened or lowered as a function of the direction of electric current flow.
The electric windings are controlled via an appropriate control device as a function of signals of a sensor that detects the axial deviation of the rotor from its theoretical ideal or pre-calculated position. Thus, a control current is brought about upon an external, axial loading of the rotor which control current generates an opposing electromagnetic force corresponding to this external loading. This known type of control requires a high sensor precision that can only be achieved with very complicated and correspondingly expensive sensors.
German Patent Publication DE 31 30 974 A1 describes a similarly designed magnetic bearing arrangement for an open-end spinning device. Like the previously described device, this known bearing arrangement comprises a control device reacting to a sensor signal and comprises at least one electromagnet controlled by this control device for producing an axial rotor movement. A speed sensor reacting to axial movements of the spinning rotor is used thereby as sensor.
The control device is designed so that in the theoretical position of the spinning rotor the current for the electromagnet is at least approximately zero. For this purpose, this known control device has a PD (proportional-derivative) controller with positive feedback, the input of which is connected to the speed sensor.
Even the magnetic bearing arrangement described above has not been convincing in practice in combination with open-end spinning devices. In particular, the use of a speed sensor has proved to be problematic since such sensors react extremely sensitively to magnetic interference fields like those that are almost unavoidable in conjunction with individual electric motor drives.
Moreover, German Patent Publication DE 198 27 606 A1 teaches a magnetic bearing arrangement in which the rotor shaft of the spinning rotor is supported without contact in two permanent magnet pairs arranged at an axial spacing. The permanent magnet pairs are designed so that unequal magnet poles are opposite each other. In order to maintain a central axial position of the spinning rotor, an electromagnetic central position control is also provided. In particular, the axial central position control of the spinning rotor takes place by an appropriate, purposeful supply of current to at least one coil arranged in the vicinity of the stator permanent magnet. Additionally, a preferred direction of fall of the spinning rotor is realized in this known magnetic bearing device by an appropriate magnetic designing of the front and rear magnetic bearing components.
In view of the state of the art discussed above, it is accordingly an object of the present invention to develop a method of frictionless operation of a magnetic bearing arrangement for open-end spinning devices in which the magnetic bearing arrangement should be economical to manufacture and also reliable during operation.
The invention addresses this objective by providing an improved method of operating an open-end spinning device having a spinning rotor supported by a rotor shaft both radially and axially in a magnetic bearing arrangement comprising spaced permanent magnet pairs and an electromagnetic central position control device comprising a sensor device and a pair of actor coils that can be supplied with current in a defined manner. According to the present invention, the method comprises the processing of a signal of a rotor position sensor in the central position control device by initiating a coil current by a controller and initially regulating the coil current toward zero by negative feedback of an integrator. Subsequently, a positive feedback of the coil current is produced by negating an input signal of the integrator which positive feedback results in an at least intermittent increase of the coil current in the actor coils and thereby lifts the spinning rotor from its axial catch bearing and transfers the spinning rotor into its operating position. Thereafter, the coil current in the actor coils is regulated back toward zero in the operating position of the spinning rotor.
The method in accordance with the invention has the particular advantage that a simple and economic position sensor can be used for detecting the position of the magnetically supported spinning rotor which sensor must meet only relatively low requirements, especially as regards the precision and stability of the zero or neutral point. That is, the control device utilized in the present invention first processes the signal of the bearing sensor in such a manner that a negative feedback of the coil current is initiated by the integrator, that has the result that after only a short time the coil current is adjusted in the actors with sufficient precision toward zero. The negation of the input signal of the integrator subsequently results in a positive regenerative feedback in the control loop and therewith in a rise of current in the actor coil or coils, as a result of which the spinning rotor is lifted off of its axial catch bearing and adjusted into its operating position in which the coil current in the actors again moves toward zero.
The position sensor is designed as an inductive sensor whose output signal can be processed by a PD controller and an integrator and whose input signal can be negated in a simple manner for controlling the actors, that can be supplied with current, of the central position control device.
In a preferred embodiment, the position sensor generates an output signal whose value is directly proportional to the spacing between the rotor-shaft end and the position sensor.
Interference signals are preferably minimized by a filter/amplifier unit that is connected between the position sensor and the PD controller. The PD controller is advantageously connected on the output side via a power amplifier to the actors and to the integrator.
Moreover, in a preferred embodiment the integrator is connected on the input side to a negation unit and to offset input means.
The input signal of the integrator can be simply and reliably processed in such a manner via the negation unit in conjunction with the offset input means that a positive feedback of the coil current is produced, which finally results in a reliable lifting of the spinning rotor from its axial catch bearing. The offset input means thereby unambiguously defines the polarity of the coil current and therewith the direction of force so that a reliable lifting of the spinning rotor from its axial catch bearing is assured at all times.
An alternative design is also possible in which the input signal of the integrator is derived directly from the output signal of the PD controller or directly from the output signal of the filter/ amplifier unit.
Instead of a negation unit it can also be provided that the integrator can be connected on the input side to a point in the control loop which point has a negation of the signal. That is, the integrator can be connected via an appropriate connecting means directly to the output, which is negated in such an instance, of the filter/amplifier unit or to the negated output of the PD controller.
A possible design variant of the invention also consists in deriving the input signal of the integrator directly from the position sensor.